Macromolecules 1992,25, 530-534
530
Benzonorbornadiene End Caps for PMR Resins Michael J. Panigot,t J o h n F. Waters,tJ Uday VardeJ James K.Sutter? and Chaim N. Sukenik'9t Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106, and Polymer Science Branch, NASA Lewis Research Center, Cleveland, Ohio 44135 Received May 21, 1991;Revised Manuscript Received September 9, 1991
ABSTRACT Several ortho-disubstituted benzonorbornadiene derivatives are described. These molecules contain acid, ester, or anhydride functionality permitting their use as end caps in P M R (polymerization of monomer reactants) polyimide systems. The replacement of the currently used norbomenyl end caps with benzonorbornadienyl end caps affords resins of increased aromatic content. It also allows evaluation of some mechanistic aspects of PMR cross-linking. Initial testing of N-phenylimide model compounds and of actual resin formulations using the benzonorbornadienyl end cap reveals that they undergo efficient thermal crosslinkingto give oligomerswith physical properties and thermal stabilitycomparableto commercialnorbomene-
end-capped P M R systems.
PMR-15 (polymerization of monomer reactants), developed jointly by NASA and TRW,' is a commercially important polyimide-based composite with good high-temperature properties. Imidization of the indicated monomers (eq 1) is followed by a higher temperature curing.
MDA; n + 1 equiv
nadic end cap; 2 equiv
0
o
0
0
m
0
0 BTDA; n
equiv
The molecular weight of the resin is controlled by endcapping molecules which are also responsible for crosslinking the cured composite. Despite its commercial success, lowering the cross-linking temperature and/or improving the thermal stability of the PMR resin are still important research and development goals.lb Since the cross-linking of these polyimide oligomers occurs through their end caps and since it has been demonstrated that the nadic end cap contributes the most to the thermal decomposition of PMR resins,lc we have approached the study and improvement of PMR-16 by modifying its norbomenyl end cap. Modification involving the substitution of both the bridgehead and vinyl positions of the norbornenyl ring has been reported elsewhere.2 We herein address the use of benzonorbornadienyl end caps. Benzonorbomadienyl incorporation should have a number of ramifications: (1)replacing the substituted succinic acid derivative of the nadic end cap with a phthalic acid derived unit should give the end cap imide-forming reactivity more comparable to that of the BTDA units (eq 1) providing a more predictable distribution of oligomer molecular weight; (2) the retro-Dieb-Alder (RDA)reaction that is readily available to the norbornenyl end cap3would
* Author to whom correspondenceshould be addressed. f
Case Western Reserve University. NASA Lewis Research Center.
0024-929719212225-0530$03.00/0
be strongly disfavored; (3)benzonorbornadienes raise the possibility of photochemical reactivity in terms of possible photopolymerization and in terms of end-cap rearrangement via the di-?r-methane reaction4 that is unavailable to norbornenes; (4) if the cross-linking of such imide oligomers could still be achieved by chemistry other than RDA reactions, the resulting resins should have increased aromatic content. To the extent that RDA chemistry has been implicated in the thermal polymerization of PMR15: preventing such reactions might impair the crosslinking of such systems. However, if the thermal crosslinking of the polyimide oligomers still occurred, then preventing RDA reaction and increasing aromatic content might contribute to better high-temperature resin stability.6 To allow proper consideration of these issues, an efficient synthesis of suitably substituted benzonorbomadienes had to be developed. Two complementary options are the cycloaddition reactions shown below. Reaction of the indicated bicyclotriene with dimethyl acetylenedicarbox~ the reaction ylate (eq 2) has been r e p ~ r t e d .Alternatively, of cyclopentadiene with substituted benzynes (eq 3; A = acid or its equivalent) has strong a n a l ~ g y . ~
h
COOMe
We report herein an efficient synthesis of the benzonorbornadienyl end cap and its use in PMR resin formulations and (as an N-phenylimide) in model studies. The photochemistry of these compounds is described in a separate paper presently in preparati~n.~ Results A. Synthesesof Monomers and Model Compounds. The diester synthesis shown in eq 2 was adequate for the production of small samples of the desired end-capping material,l0but it is a low-yield process that is not amenable to scale-up. On the other hand, dibromobenzyne generation and its addition to cyclopentadiene (modeled after Hart et al."), followed by cyanation of the dibromoben1992 American Chemical Society
Benzonorbornadiene End Caps for PMR Resins 531
Macromolecules, Vol. 25, No. 2, 1992 Scheme I
Q
+
"'aBr&
Br
Br
CuCN
Br
Br
'COOH
CN
I
zonorbornadieneand hydrolysis of the dinitrile to diacid I, proved to be more practical (Scheme I). Alternative implementations of this scheme (different substituents and/or different benzyne precursors) were less successful.12 Compound I served as the starting material for the two substituted benzonorbornadienes needed for this study. It was convertedto anhydride I1which can be used directly
..
11
111
or after methanolysis to its half-acid half-ester as a PMR end cap. Also, I, its diester, or anhydride, could be used to make N-phenylimide I11 for use as a model compound with which to study the thermal chemistry of the end cap and compare it to the corresponding nadic N-phenylimide IV.2J3 B. T h e r m a l Chemistry a n d Testing of Model Compounds. Thermal cross-linking of benzonorbornadiene units was studied by comparing the behavior of I11 and IV by a combination of DSC, NMR, and SEC measurements. DSC experiments on the two isomers of IVI3(endo and exo ring junctions) each show sharp endotherms at their respective melting points and a strong, higher temperature exotherm whose onset coincides with the high-temperature cure of the PMR resin. Similarly, the DSC of I11 shows the onset of endothermic activity at 147.4"C (peak at 161.9"C) and a strong exotherm starting at 308.4 "C which peaks at 351.5 "C. Samples of I11 and IV which had been heated (as neat solids) to 250 "C showed a steady disappearance of vinyl protons in their solution NMR spectra. The comparison of aromatic to nonaromatic material in cured sampleswas done by l3C NMR, and it showed a steady increase in the relative amount of aromatic carbons as the heating of the samples of I11 proceeded. In the heating of IV, no corresponding increase in the relative aromatic content was observed. Also, as part of the effort to characterize the mixture of materials formed by heating 111, as much as 10% of the dihydro compound V was isolated. None of the corresponding hydrogenated analogues of IV was found in any of its thermolysis experiments.
V
Table I Extent of Polymerization of I11 and IV. entry temp, "C time, h ?6 oligomer I11 % oligomer IV 96 75 32 1 195 1 41 (41)* 7 (14)b (2)' 2 250 3 2 56 (52)b 12 (24)b(2)' 4 4 69 (71)b 74 (71)"(11)' 5 24 83 93 6 120,144 98 1 79 10 7 285 2 88 32 8 9 3 92 72 10 4 94 79 11 15 98 95 12 24 99 97 13 330 1 98 96 a Reactionsdone in glass tubes sealed under 50-mmvacuum (unless otherwise indicated): temperature, f 5 O C , time, *2 min. b Reactions done under ambient pressure of argon. e Sealed under 1.5 x m m vacuum. ~
The extent of thermal oligomerization of I11 at various times and temperatures, as well as a profile of oligomer size and distribution, was determined by size-exclusion chromatography (SEC). Table I reports the progress of oligomer formation from heating neat samples (sealed tube, reduced pressure or inert atmosphere) of I11 and of IV. SEC analysis was facilitated by the solubility in THF of these model end caps and their thermal products. Table I1 reports the characterization of these oligomers. These data highlight the similarity of I11 and IV with regard to the size and polydispersity of the oligomers formed. However, two differences in oligomerization kinetics should be noted. First, entries 2-4 (Table I) indicate that while polymerization of the benzonorbornadienylunit in I11 is pressure independent, this is not true for the norbornenyl imide. Second, there is a discontinuity in the rate of oligomer formation from IV that is not seen with 111. Comparing entries 3 to 4 and 8 to 9 (Table I) suggests an induction period for the cross-linking of IV that is not seen for 111. C. Formulation and Testing of Molding Powder and Resin Disks. Thermal analyses and analyses of the thermooxidative stability of the cross-linked, benzonorbornadiene-end-capped polyimides were performed on molding powders and resin disks. The molding powders were prepared from 11, BTDA, and MDA by chemistry analogous to that shown in eq 1 (n = 2)and were held at 260 "C (500 O F ) for 1 h after imidization was complete. The resin disks were prepared by heating molding powders under pressure in a die. DSC analysis (40 "C/min) of molding powders using I1 as the end cap showed the onset of exothermic activity at 375 "C, consistent with the behavior of the corresponding model compound (111). Rheological testing data were used to assess the viscosity of the heated molding powders as a function of temperature. These tests showed that the commercial PMR-15 system (Hysol brand) melts at 225 "C and polymerizes at 300 "C. Molding powders using I1 as the end cap both melted and polymerized at approximately 50 "C higher temperature. Resin disks were tested in the following ways. Thermogravimetric analysis (TGA,10 "C/min) provided some information about the thermal stability of the modified polyimides. These data indicated that weight loss began at 494 "C, compared to 460 "C for PMR-15.1C Thermomechanical analysis (TMA) of the benzonorbornadienyl resin disks showed a glass transition temperature (T,)of 222 "C, while that of a commercial PMR-15 disk is 275 "C. The thermooxidative stability of the resin disks was tested with an isothermal weight loss experiment for lo00
532 Panigot et al.
Macromolecules, Vol. 25, No. 2, 1992 Table I1 Oligomer Characterization for 111 and IVa
Mn (M entry
temp ("C)/time(h)
4 5 6 7 8 9 10 11 12
13 (I
I11 2310 (8.1) 2040 (7.1) 1970 (6.9) 1880 (6.5) 2190 (7.6) 2110 (7.4) 1880 (6.5) 2080 (7.2) 1730 (6.0) 1760 (6.1) 1790 (6.2) 1720 (6.0) 1630 (5.7)
195196 25011 25012 25014 250124 2501120 2501144 28511 28514 285115 285124 33011 33012
1 2 3
PDI
MW
IV
I11
IV
I11
IV
1330 (5.6) 1340 (5.6) 1420 (5.6) 1540 (6.4) 1530 (6.3)
2800 3320 2280 2280 2590 2470 2170 2460 2230 2180 2230 2100 2000
1650 1340 1920 1920 1990
1.21
1.24 1.24 1.24 1.25 1.30
1390 (5.8) 1400 (5.9) 1530 (6.4) 1500 (6.3) 1790 (7.5) 1280 (6.1)
1770 1750 1820 2000 2150 1450
1.63 1.20 1.21 1.18
1.17 1.15 1.18 1.29 1.24 1.24
1.28 1.25
1.19 1.33 1.20 1.13
1.22
1.23
Temperatures are f 5 "C; times are f 2 min. Samples were heated in glass tubes sealed under 50-mm vacuum. Table 111 Weight Loss for Resin Disks Aged at 600 OF (316 "C)
Scheme I1 0.
weight loss, ?6 polyimide nadic/BTDA/ MDA Hysolbrand resin II/BTDA/ MDA
postcure
250h
500h
750h
1OOOh
1.0 f 0.2 4.4 f 0.2 6.6 f 0.1 10.7 f 0.5 14.8 f 0.3
0.8fO.2 3.8f0.2 5.8f0.3
9.0f0.5 12.5f0.5
1.8f 0.1 3.2f 0.3 5.4 f 0.2
9.3 f0.6 12.9f0.6
h at 316 "C (600 O F ) . Similar size resin samples were weighed and placed in open vials which were then heated in a thermostated oven, and samples were removed and reweighed a t 250-h intervals. Since the melting and polymerization temperatures of the nadic end cap and of I1 are different, resins with these different end caps may have different optimal curing conditions. However, since PMR-15 is cross-linked a t 600 O F for 2 h at 1000 psi following an atmospheric pressure staging a t 260 "C,these conditions were also used for the system end capped with I1 (Table 111). These data (each reflecting an average of a t least three independent determinations) clearly show that resins end capped with I1can achievethermal stability comparable to that of a PMR-15 polyimide.
Discussion Despite the lack of RDA chemistry, benzonorbornadienyl end caps cross-link to give oligomers whose size and properties are comparable to commercial nadic systems. The lack of pressure dependence in the oligomerization of I11 probably reflects this absence of RDA reaction. The increased aromatic content of cross-linked I11 and the recovery of V from these samples are both consistent with a cure mechanism involving initial cleavage to a diradical (Scheme 11). The formation of radical VI is one possible fate of such a diradical. This loss of a hydrogen atom would contribute to the aromatic content of the resins and provide a basis for the hydrogenation of I11 to V. The initial diradical could also isomerize (H shift) to methylnaphthalene derivatives, affording a further increase in the aromatic content. The practical use of end caps such as I1 depends on the performance advantage they offer in terms of thermal and mechanical properties and in terms of ease of processing. The DSC measurements of the model end cap I11 and of the benzonorbornadienyl containing molding powder show that thermal cross-linking of the end cap occurs and the SEC measurements indicate that heating I11 yields oligomers (n= 6-7) comparable to those formed from heating the nadic model IV. The TGA and TOS data also suggest
111
I+.'
Lv
H
I
-4
ti
H abstraaion
VI
that a performance comparable to that achieved with nadic end caps should be available with our benzannulated analogue. Further testing of both the mechanical properties and the thermal stability of such new resins and composites is still needed. Interms of resin processing,these materials should offer the advantage of cure temperatures that are comparable to those of current PMR technology without the need for the high-pressure processing characteristic of the nadic end cap. Moreover, the imidization of a benzannulated end cap leads to phthalimides analogous to those from BTDA. Thus, while further work is needed to optimize the processing conditions for this new end cap, imidization of such resins is likely to be more uniform, with less triester formation or residual anhydride, than current nadic systems. Experimental Section General Procedures. NMR spectra are reported in 6 units and were recorded on a Varian XL-200 spectrometer in CDCla solvent (unless otherwise noted). 'H NMR spectra (200 MHz) in CDC13are referenced to CHCl3at 7.24 ppm. 13CNMR spectra (50 MHz) are referenced to the solvent triplet centered at 77.0
Macromolecules, Vol. 25, No. 2, 1992 ppm. Infrared spectra were run on a Mattson Cygnus 25 FTIR equipped with a water-cooled source and a TGS detector (4-cm-l resolution). High-resolution mass spectra (EI) were run on a Kratos MS 25RFA spectrometer. UV-visible spectra were run in CH3CN in quartz cuvettes with a path length of 1cm on a Cary 2300 UV-visible spectrophotometer connected to a DS-15 work station. HPLC used a Waters 590 pump equipped with a Rheodyne 7125 injector and a Waters 401 differential refractometer or an ISCO V4 UV-visible detector. TLC was done on aluminumbacked 0.2-mm 60F254 silica gel plates from EM Science using phosphomolybdic acid or UV light for visualization. Column chromatography was done with silicagel (Aldrich,230-400 mesh). General Procedure for N-Phenylimide Polymerization Studies. Samples of I11 and IV (3-5 mg) were sealed (after three freeze/thaw cycles) under a 50- or 0.0015-mm vacuum, or under argon at ambient pressure, in untreated thick-walled (1.5-mm) Pyrex glass tubes. The tubes were then immersed in a sand bath maintained at constant temperature. Tubes were withdrawn, cooled, opened, and assayed by NMR and SEC. SEC was run at 1 mL/min in T H F using an IBM LC/9533 pump, IBM U1trastyragel columns A and C, and a UV-vis detector. Numberaverage and weight-average molecular weights and the polydispersity index were determined using the Chromatochart program (Interactive Microwave) on an Apple IIe personal computer. Molecular weights were calculated from calibration curves which were obtained using polystyrene standards. From these same experiments, the extent of polymerization was determined using a cut and weigh technique. An average of three copies of the GPC trace was used, and the extent of polymerization was determined by the weight of the GPC trace for polymeric material divided by the total weight of the GPC trace for monomer and polymer. General Procedures for Thermal Studies. Differential scanning calorimetry was run on either a Du Pont Model 910 or a Perkin-Elmer 7 Series differential scanning calorimeter under air pressure at a rate of 10 OC/min (unless otherwise specified) from 20 to 500 OC. The data were processed using the Omnitherm ATVmtage I1 thermal analysis program on an IBM personal computer. Thermogravimetric analysis and thermomechanical analysis were run on a Perkin-Elmer 7 Series thermal analysis system and were run at a rate of 10 OC/min from 20 to 700 OC. Molding powders were prepared by combining the calculated amounts of n + 1equiv of diamine, n equiv of dianhydride, and 2 equiv of end cap in 30 mL of acetic acid and heating to reflux overnight and then adding 5 mL of acetic anhydride and refluxing for an additional 3 h to ensure complete imidization. The molding powder is isolated by filtration and dried in a vacuum oven at 100 OC. Staging of the molding powder at 260 "C for 1 h, open to the air, assured complete removal of volatiles. Resin disks were prepared by placing the molding powder in a die, heating the die to between 288 and 399 OC under 1000psi pressure for 2 h, and then cutting for use in the various thermal analyses. For the thermooxidative stability studies, samples with a surface area of 40-60 cm2 were used. Chemicals. 3,3',4,4'-Benzophenonetetracarboxylic dianhydride (Aldrich), DDQ (Sigma), dimethyl acetylenedicarboxylate (Aldrich), 1,2,4,5-tetrabromobenzene(Aldrich), and copper cyanide (Aldrich)were used as received. DMF (Fisher) was vacuum distilled from molecular sieves. Hexane for flash chromatography was distilled prior to use. Aniline (Fisher) was vacuum distilled from CaH2. Dry THF and ether were distilled from sodium. HPLC-grade hexane was used as received for preparative HPLC. Bis(4-aminopheny1)methane (Eastman) was recrystallized from benzene prior to use. 6,7-Bis(carbomethoxy)benzonorbornadienewas synthesized by combining 5,6-dimethylenebicyc10[2.2.1]hept-2-ene (1 g, 8.47 mmol),14dimethyl acetylenedicarboxylate (2.4 g, 16.94 mmol), and 40 mg of hydroquinone in a thick-walled (1.5-mm) Pyrex glass tube which was heated in an oil bath at 80 "C for 3 days (Caution! In other experiments, heating to higher temperatures resulted in rupture of the glass tube). The resulting product was dissolved in 15 mL of benzene and added dropwise (18.93g, 8.47 mmol) to 2,3-dichloro-5,6-dicyano-1,4-benzoquinone cooled in an ice bath. The reaction mixture was stirred in an ice bath (2 h) and then at room temperature overnight. The precipitate was filtered and washed with 100mL of benzene. The
Benzonorbornadiene End Caps for PMR Resins 533 combined organic layers were concentrated and passed through a column (15 X 5 cm) of alumina with benzene (800 mL) as eluant. The eluant was concentrated and further purified by flash chromatography (silicagel, 20 % ethyl acetate in heptane, Rf0.2): 'H NMR 6 7.5 (8, 2 HI, 6.75 (t,2 H, J = 1.9 Hz), 3.93 (t, 2 H, J=l.8Hz),3.86(~,6H),2.34,2.23(ABq,2H,J=7.55Hz) [lit.' 'H NMR 6 7.43, 6.66, 3.86, 3.76, 2.31, 2.181. 6,7-Dibromobenzonorbornadiene.To a three-neck 5-L flask fitted witha mechanical stirrer, 250-mL addition funnel, Nz inlet, and septum were added 1,2,4,5-tetrabromobenzene(50 g, 0.127 mol) and 2.25 L of dry toluene. The mixture was cooled to -78 OC and 87 mL of a 1.6 M solution of n-butyllithium in hexane (140mmol) was added over a period of 45 min. After an additional 25 min, 14.7 g (222 mmol) of freshly cracked cyclopentadiene was added. The mixture was kept at -78 "C for 1.5 h and then allowed to come to room temperature overnight. The reaction was quenched by the addition of CH30H (10 mL). The toluene solution was washed with 500 mL of water, and the aqueous layer was extracted with 2 X 200 mL of ether. The combined organic extracts were dried over MgSO4, concentrated to a yellow oil, and chromatographed (hexane) to yield 22.1 g (58%) of waxy white solid Rf 0.38 (hexane); IR (CCL) 3073,2992,2977,2940, 2865,1448,1434,1355,1303,1226,1082,913,878,607 cm-l; lH NMR 6 7.43 (8, 2 H), 6.74 (br s, 2 H), 3.83 (br s, 2 H), 2.28, 2.20 (ABq, 2 H, Jm = 7.4 Hz); 13C NMR 6 153.1, 142.6,126.6, 119.3, 69.5,49.9. A small sample was recrystallized from CHsOH, mp 61-63 OC. High-resolution mass. Calcd for CIIHJ3r2: 297.8992. Found: 297.8951. 6,7-Dicyanobenzonorbornadiene.To a solution of 6,7-dibromobenzonorbornadiene (15.5 g, 51.6 mmol) in dry DMF (155 mL) was added CuCN (11.5 g, 129 mmol). The mixture was heated at reflux for 16 h, allowed to cool, and poured into concentrated aqueous NH40H (200 mL). Water (600 mL) was added, and the entire aqueous solution was extracted with ether (2 x 400 mL). The combined ether extracts were washed (3 X 500 mL) with 1:3 NHdOH/water until the blue in the aqueous layer disappeared. The organic layer was dried over MgSO,, and solvent was removed. Flash chromatography (1:3 EtOAc/hexane) of the greenish residue yielded 3.4 g (34%) of a white crystalline solid: mp 111-113 OC; lH NMR 6 7.55 (s,2 H), 6.81 (t,2 H, J = 1.8 Hz) 4.02 (t, 2 H, J = 1.8 Hz), 2.42, 2.29 (ABq, 2 H, JAB = 7.87 Hz); 13CNMR 6 158.9, 142.6, 125.3, 116.1, 112.2, 70.0, 50.3; Rf (20% EtOAc/hexane) 0.2; IR (CC4) 2997, 2992, 2980, 2234, 1461, 1303, 1227, 901 cm-l. High-resolution mass. Calcd for ClsHaN2: 192.0688. Found: 192.0696. Benzonorbornadiene-6,7-dicarboxylicAcid (I). 6,7-Dicyanobenzonorbornadiene (332 mg, 1.73 mmol) was suspended in 4 mL of 6 N aqueous KOH, refluxed for 8 h, cooled to room temperature, acidified to pH 1with 20% HC1, and continuously extracted with CH2C12 for 8 h. The CHZClz layer was dried (MgSO,) and solvent removed to give a nearly quantitative yield ofawhitepowder: mp 17OOC (lit.'mp178OC);lHNMR (acetone&) 6 7.44 (s,2 H), 6.69 (br s, 2 H), 3.86 (br s, 2 H), 2.19,2.06 (ABq, 2 H, JAB= 7.7 Hz); IR (KBr) 1670 cm-l; UV,,A 219 nm, log t 3.98. High-resolution mass. Calcd for C13H1004: 230.0579. Found 230.0579. Benzonorbornadiene-6,7-dicarboxylic Anhydride (11). Benzonorbornadiene-6,7-dicarboxylic acid (3.8g, 16.5 mmol) was heated in acetic anhydride (75 mL) at reflux for 2 h. The mixture was allowed to cool, and acetic anhydride was removed under vacuum. The crude brown solid was filtered through silica gel (CHCl3) to yield 2.874 g (82 % ) of a white crystalline solid, mp 120-121 OC. A small sample was further purified by sublimation [90OC (0.1 mmHg)]: lH NMR 6 2.35,2.49 (ABq, 2 H, Jm = 7.8 Hz); 4.08 (t, 2 H, J = 1.9 Hz); 6.82 (t, 2 H, J = 1.9 Hz); 7.70 (8, 2 H); 13C NMR6 50.50,70.07,117.51,129.24,142.68,162.65,163.26; IR (CC4) 3000,2980,2940,1850,1780, 1450,1390, 1285,1165, 1090,1075,1000,895cm-l; UV X 299 nm, log t 3.39; A,, 234 nm, log e 4.33. High-resolution mass. Calcd for C13H803: 212.0473. Found: 212.0468. N-Phenyl-6,7-benzonorbornadienecarboximide(111). Aniline (10 mL, 10.22 g, 110 mmol) and benzonorbornadiene6,7-dicarboxylic acid (2 g, 8.7 mmol) were heated at 130 OC for 17 h, cooled, diluted with ether (75 mL), and washed with 2 X 100 mL of 5% HC1. The crude imide was dissolved in CHzClZ, treated with decolorizing carbon, and filtered, and the solvent
534 Panigot et al.
Macromolecules, Vol. 25, No. 2, 1992
Series 282;American Chemical Society: Washington, DC, pp 53-61. (3) For reviews of retro-Diels-Alder chemistry, see: Kwart, H.; King, K. Chem. Reu. 1968,68,415-447.Ripoli, J. L.; Rouessac, A.; Rouessac, F. Tetrahedron 1978,34,19-40. (4) (a) Edman, J. R. J. Am. Chem. SOC.1966,88,3454-3455.(b) Edman, J. R. J. Am. Chem. SOC.1969,91,7103-7107. (5) Bums, E. A.; Jones, R. J.; Vaughan, R. W.; Kendrick, W. P. 2,3-Dihydro-N-phenylbenzonorbornadiene-6,7-dicarboxNASA CR-72633,1970. imide (V)was synthesized by dissolving I11 (50 mg) in EtOH (6)Critchley, J. P.;Knight, G. J.; Wright, W. W. Heat Resistant Polymers; Plenum Press: New York, 1983;pp 125-181. (200mL) and adding Pd/C (5mg). Low-pressure hydrogenation (7) Butler, D. N.; Snow, R. A. Can. J . Chem. 1975,53,256-262. was complete within 24 h. The reaction mixture was centrifuged (8) (a) Snow, R. A.; Cottrell, D. M.; Paquette, L. A. J. Am. Chem. to separate the catalyst which was rinsed with fresh EtOH (50 SOC.1977,99,3734-3744.(b) Paquette, L. A.; Cottrell, D. M.; mL). Thecombined solutions were concentrated, and the product Snow, R. A. J . Am. Chem. SOC.1977,99,3723-3733. (c) Pawas purified by preparative TLC (25% ethyl acetate in hexane, quette, L. A.; Ku, A. y.; Santiago, C.; Rozeboom, M. D.; Houk, Rf 0.25). Since only a small amount of purified material was K. N. J . Am. Chem. SOC.1979,101,5972-5980.(d) Tanida, needed, no attempt was made to maximize, or even determine, H.; Muneyuki, R.; Tsuji, T. Bull. Chem. SOC.Jpn. 1964,37, the yield of this reaction: lH NMR 6 7.54 (s,2H), 7.48-7.08 (m, 40-43. (9) Panigot, M. J.; Gano, J. E.; Sukenik, C. N., manuscript in 5 H), 3.46 ( 8 , 2 H), 1.64 (d, J = 3 Hz,1 H), 1.45 (d, J = 3 Hz, 1 preparation. H),1.42 (d, d, J = 18 Hz,4 Hz,1 H); 13CNMR 6 173.10,160.99, 137.14,135.42,134.23,132.99,131.74,121.20,54.55,49.19,31.40; (10) Varde, U. Ph.D. Thesis, Case Western Reserve University, 1986. mp 150 OC. High-resolution mass. Calcd for C19H15N02: (11) (a) Hart, H.; Lai, CY.; Nwogoku, G.; Shamouilian, S.;Teu289.0850. Found 289.0856. erstein, A.; Zlotogorski, C. J. Am. Chem. SOC.1980,102,6649N-Phenylbicyclo[2.2.l]hept-2-ene-5,6-dicarboximide (IV) 6651. (b)Hart, H.; Shamouilian,S.; Takehira,Y. J . Org. Chem. was synthesized by the method of Wong and Ritchey from N1981,46,4427-4432.(c)Hart, H.; Nwogoku, G. C. Tetrahedron phenylmaleimide and cyc10pentadiene.l~The endo isomer thus Lett. 1983,24, 5721-5724. (d) Nwogoku, G. C.; Hart, H. producedshowedmp 140-141 "C (lit.13mp 140-141 OC): 'HNMR Tetrahedron Lett. 1983,24,5725-5726.(e) Harada, K.; Hart, H.; Du, C.-J. F. J. Org. Chem. 1986,50,5524-5528. (f) Hart, 6 7.46-7.09 (m, 5 H), 6.24 (t, 2 H, J = 1.8 Hz), 3.4-3.5 (m, 4 H), H.; Bashir-Hashemi, A,; Luo, J.; Meador, M. A. Tetrahedron 1.76,1.59(ABq, 2 H, J = 8.7 Hz).The exo isomer was obtained 1986,42,1641-1654. (g) Hart, H.; Lai, C.-Y.; Nwogoku,G. C.; by heating the endo isomer (195OC/15h) to obtain an endo/exo Shamouilian, S. Tetrahedron 1987,43,5203-5224. mixture. Pure exo isomer was obtained by preparative HPLC (12) Panigot, M. J.Ph.D. Thesis, Case Westem Reserve University, (CHzC12eluant): mp 198-199 "C (lit.13mp 198-199 OC);lH NMR 1991. 6 7.22-7.50 (m, 5 H),6.33 (t, 2 H, J = 1.8Hz),3.39 (t,2 H,J = (13) (a) Wong, A. C.; Ritchey, W. M. Macromolecules 1981,14, 1.6 Hz), 2.83 (d, 2 H, J = 1.3 Hz),1.66,1.42 (ABq, 2 H, J = 9.9 825-831. (b) Wong, A. C.; Garroway, A. N.; Ritchey, W. M. Hz). Macromolecules 1981,14,832-836. (c) Hay, J. N.; Boyle, J. D.; Parker, S.F.; Wilson, D. Polymer 1989,30,1032-1040. (d) Malhotra, V. Ph.D. Thesis, Case Westem Reserve University, Acknowledgment. Support from NASA for the work 1984. at CWRU (Graduate Researcher Fellowshipto M.J.P. and (14) King, R. B.; Stone, F. G. A. J . Am. Chem. SOC.1961,83,3590NASA LeRC research contract to C.N.S.)is gratefully 3593. removed to yield the desired N-phenylimide (2.29g, 92% 1: lH NMR 6 7.62 (8, 2 H),7.44-7.22 (m, 5 H),6.74 (t, J = 5 Hz,2 H), 3.97 (m, 2 H), 2.38 (d, J = 3 Hz, 1 H), 2.24 (d, J = 3 Hz, 1 H); l3C NMR 6 164.71,160.05,143.14,132.16,129.41,128.63,127.84, 127.06,116.47,70.20,49.80; m p 144-150 OC; IR (KBr) cm-'; UV A,, = 240 nm, log e = 4.60. High-resolution mass. Calcd for ClsHl3NOz: 287.0744. Found: 287.0750.
acknowledged.
References and Notes (1) (a) Serafhi, T.T.; Delvigs, P.; Lightsey, G. R. J. Appl. Polym. Sci.1972,16,905-915.(b) Wilson, D. Br. Polym. J. 1988,20, 405-416. (c) Vannucci, R. D. SAMPE Q. 1987,19,31. (d)
PMR refers to the in situ polymerizationof monomer reactants, and PMR-15 refers to a formulated molecular weight of 1500. (2) Sukenik, C. N.; Malhotra, V.; Varde, U. In Reactiue Oligomers; Harris, F. W., Spinelli, H. J., Eds.; ACS Symposium
Registry No. I, 56306-44-6;11,137495-56-8; 111,137467-22-2;
I11 (homopolymer), 137467-23-3; IV,2623446-8;IV (homopolymer), 31533-50-3;V, 137495-55-7;(II)[(BTDA)(MDA)l, (homopolymer), 137515-58-3; 6,7-bis(carbomethoxy)benzonorbornadiene, 56306-25-3;5,6-dimethylenebicyclo[2.2.l]hept-2-ene, 5628-77-3; dimethyl acetylenedicarboxylate, 762-42-5; 6,7-dibromobenzonorbornadiene, 137495-57-9;1,2,4,5-tetrabromobenne, 636-282;cyclopentadiene, 542-92-7; 6,7-dicyanobenzonorbomadiene, 137495-58-0.
